Crawl space insulation: how to insulate the right way

HVAC Logo IconBy Tom MoorAugust 1, 2023
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Insulating crawl space areas in your house improves the home’s overall energy efficiency. Complementing your investment in a modern heating and cooling system with adequate crawl space insulation may offer lower energy costs and a more comfortable home.

Whether your crawl space is ventilated, unventilated, or you’re not sure you recognize the difference, we’re here to help. We’ll share why insulating your crawl space matters and how you can improve or replace your home’s old insulation.

crawl space insulation

What is crawl space insulation?

Crawl space insulation helps maintain your home’s energy efficiency by preventing the loss of warm and cool air through your flooring. If your floor feels cold against your feet during the winter, it may be because your crawl space doesn’t have proper insulation to keep the heat in.

Insulation comes in a few different forms. Some of the most popular options are fiberglass batts, rigid foam boards, and foam spray.

How does insulation work?

Insulation traps pockets of air to slow the movement of heat going in and out of your home. The rate in which the heat is slowed is measured by an R-value.

The goal is to envelop your home in thermal protection to keep you comfortable all year round.

What is an R-value?

R-value of insulation refers to its thermal resistance. Your insulation material’s resistance to heat is measured by the R-value. The higher the R-value, the better the material is at insulating crawl spaces.

The R-value depends on the density of your insulation, the type you use, and its thickness. Other measurement factors may also include the age of the insulation, temperature, and moisture accumulation. When calculating the R-value of a multilayered installation, the technician will add together the score from each category to get a final value.

Insulating your home saves money

Many homeowners can save on energy bills by simply adding or updating their insulation. If you live in an older home, you may not see much insulation at all. If that’s the case, you will want to add to or replace what you currently have.

Enveloping your home in insulation is one of the most cost and energy-efficient choices you can make as a homeowner. The US Department of Energy estimates that, on average, a home spends 49% of its energy bill on heating and cooling. Poor insulation could lead to a portion of unnecessary energy costs.

The Department of Energy also estimates that a properly insulated home can lower your energy bill by 10 to 15%. For many homeowners, that’s nearly $200 in savings per year.

Does crawl space insulation need to be replaced?

Damp or dangling insulation is a sure sign that your crawl space needs a revamp. If your home was built before 1990, it’s likely not up to today’s energy-conserving building codes. You may have very little to no crawl space insulation remaining

Differences between ventilated and unventilated crawl spaces

When inspecting your crawl space, you’ll want to identify if the area is ventilated or unventilated. This distinction will determine what type of insulation you need.

Ventilated crawl spaces

A ventilated crawl space helps eliminate excess moisture through the openings in the walls. Fiberglass insulation is a simple-to-install option for these types of spaces. Install it under the subfloor of the room above, between the floor joints. Also, insulate your ducts and pipes to keep them from freezing in the winter.

To help keep your crawl space dry and eliminate the risk of mold, cover your insulation with a vapor barrier.

Unventilated crawl spaces

If your crawl space isn’t ventilated, you should insulate the walls instead of the subfloor of the room above. This means you’ll use less insulation and eliminate the need to separately insulate your ducts and pipes.

The downside to an unventilated crawl space is that it must be airtight and able to maintain an air barrier. Otherwise, pests and water damage could disrupt your insulation. It’s best to have your access door come from inside your home through the subfloor to help maintain this air barrier.

Crawl space insulation cost

Crawl space insulation materials cost, on average, $0.30 to $2.50 per square foot. The estimated price for labor per square foot is between $0.60 to $1.30. Your pricing will vary based on your location, type of insulation, and any preliminary work that needs to be done to prepare your space. The cost to completely encapsulate your crawl space ranges from $1,500 to $15,000 with the average homeowner paying $5.500.

Where you live matters

Depending on where you’re located in the country, your insulation needs will differ. If you live in a warmer area, then you probably won’t need to defend against the below-freezing temperatures of snowy winter days.

Energy Star has mapped out recommended R-values based on where you call home.

Recommended Levels of Insulation
Zone R-value recommendations for crawl spaces
2R13 to R19
3R19 to R25h
4R25 to R30
5 to 8R25 to R30

Before you begin

While crawl space insulation can be something you tackle yourself, you may want to avoid the labor and stress and hire a professional. If you go the hiring route, professionals will take care of the installation, the cleanup, and properly dispose of your old insulation. They will also likely offer a service to spray your space to protect it from bacteria and fungicides.

If you do decide you’re up for the DIY challenge, make sure to have the proper safety equipment and tools.

Safety equipment

  • Safety glasses
  • Gloves
  • Dust mask or protective face mask
  • Flashlight or portable safety light
  • Hard hat or cap

Materials and tools

  • Insulation
  • Retractable utility knife
  • Tape measure
  • Straight edge for cutting

Safety recommendations

  • Wear gloves, safety glasses, and a protective mask when handling insulation, especially fiberglass.
  • Gather all tools and supplies to minimize trips into and out of the crawl space.
  • Work in a well-lit area so you can keep an eye on tools and hazards.
  • Drink plenty of water.
  • Wear knee pads when installation requires you to get low.
  • Watch out for nails and low hanging beams from your subfloor.

How to insulate a crawl space for your climate

Tips for all climates

The very first step in preparing your crawl space for insulation is eliminating any sources of moisture. Extend downspouts, check your gutters, and regrade your sidewalks, patios, and garden beds so water is directed away from your home.

Regardless of what your flooring is made of (earth, concrete, gravel), moisture will inevitably find its way through. Use a 6-mil polyethylene plastic to create a vapor barrier along the ground. The barrier can be covered with sand to keep it from being damaged.

For warmer climates

A 6 inch thick, R19 fiberglass batt is a great option if you live in a warmer climate and rarely see below freezing temperatures. You’ll need to ensure you have proper moisture control and mold prevention in place to keep your fiberglass from becoming damp and covered in mildew.

At roughly $1 per square foot, fiberglass batts are easy on your bank account and simple to work with. If you choose to make this a DIY project, wear proper protective equipment when dealing with fiberglass. Loose fiberglass particles can irritate your skin and lungs.

Step 1: Create proper support

Fiberglass batts should be unfaced and installed so they are in direct contact with the underside of the subfloor. Place wood lathes every 18 inches to support the batts, or use crisscrossing wire webbing. Avoid using stay rods. They compress your fiberglass and lessen its insulating abilities.

Step 2: Ventilate the crawlspace

If you already have a ventilated crawl space, you’re ahead of the game. If you would like to ventilate your space, we suggest contacting an insulation contractor. They will be able to calculate the proper amount of ventilation for your crawl space and add in new vents.

Step 3: Seal your subfloor

Seal all holes for electrical wiring and plumbing using a closed-cell spray foam insulation. Closed-cell spray provides both thermal and moisture protection. It is much more effective at filling in small spaces and tight corners than larger batts of fiberglass.

Avoid open-cell spray foam insulation. It soaks up a lot of moisture and will cause problems in the long run.

Step 4: Insulate pipes and ducts

Insulate your plumbing pipes and HVAC ducts with fiberglass batts to prevent any further heat loss or freezes.

For colder climates

The most effective way to insulate your crawl space in colder locations is to add insulation to the walls instead of the ceiling. You will also need to close your space off to the outdoors by sealing any air leaks. This keeps your pipes and HVAC ducts protected from freezing temperatures, which can conserve energy and save you money.

The best type of insulation for cold weather is rigid insulation. It’s a permanent solution as long as you establish moisture control and seal any air leaks. Professional insulation prices come in at around $5 per square foot and include all materials.

Step 1: Cover all vents

If you already have an unventilated space, then you’re good to go for this step. If you’re transitioning from ventilated to unventilated, fully remove the vents and seal the holes in your foundation. Simply closing your vents will not create a tight enough airlock.

Step 2: Insulate your foundation

Expanded polystyrene rigid foam board is a great option for your walls. It works on any masonry: concrete, block, brick, or stone.

Glue the rigid insulation board to the inside of your foundational walls. Use waterproof construction adhesive or mechanical fasteners to firmly attach them. Seal all seams with waterproof tape.

You can buy a four-by-eight-foot sheet of two-inch-thick expanded polystyrene insulation for around $26. This type of insulation has an R-value of 7.7. We recommend using at least three layers for the best heat resistance.

Step 3: Remove extra moisture

Humidity and moisture from your home will eventually cause condensation in your crawl space. It’s also likely that a plumbing leak will spring up unannounced at some point in your home’s long life.

Moisture control should be a top priority. Invest in a dehumidifier or sump pump to eliminate all traces of wetness. This will prevent mold and mildew from growing.

Step 4: Link your HVAC to your crawl space

This is an optional step, but a great way to keep your floors warm and crawl space cozy during the winter. Link your crawl space to your household HVAC system by installing vents in your home flooring.

The heated air will circulate under your floors and keep your feet warm in the winter. To save energy and money in the summer, close your vents off. There’s no need to pump extra cool air into your crawl space. It should stay cool on its own.

Things to remember

  • Insulation expands once it is unpackaged. Keep it wrapped until you are ready to use it.
  • If you compress insulation to make it fit, it will lose a lot of its R-value. Instead, measure where you’re placing the insulation and cut it to size.
  • Do not use open-cell spray foam. It easily absorbs water and will create a mess in your crawl space.
  • Always wear protective equipment when working on home improvement projects, especially when dealing with insulation materials like fiberglass.

Crawl space insulation: DIY or pro?

Adding or improving insulation in crawl space areas is tedious work that calls for the right tools and equipment. If you’re not overwhelmed with the thoughts of preparing the space, purchasing, measuring, cutting, and installing the insulation, the DIY approach may work for you.

Otherwise, rely on a local contractor or insulation professional to determine the scope of work and complete the job. You want the end result to support higher energy efficiency and lower energy bills. If you want to add a dehumidifier to your crawl space to prevent moisture damage, explore our top picks.

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